1. Field of the Invention
The present invention relates to a liquid agent for contact lens, which agent is capable of exhibiting an excellent preservative or sterilizing effect while assuring a sufficiently high degree of safety with respect to the eyes of the user.
2. Discussion of the Related Art
The contact lens worn on the eye of the user is likely to be soiled with stains such as proteins and lipids which are included in the tear fluid. These stains adhering to the contact lens not only deteriorate the wearing comfort of the contact lens as felt by the user, but also lower the eyesight of the user and cause various troubles to the eye such as hyperemia of the conjunctiva. Further, microorganisms such as bacteria adhering to the surface of the contact lens may proliferate thereon while the contact lens is stored after it is removed from the eye of the user. Such microorganisms may cause infectious diseases, giving adverse influences on the eye of the user.
In view of the above, the contact lens needs to be treated for cleaning and disinfection on a regular basis for safe and comfortable wearing thereof. In general, the contact lens is treated in the following manner. Initially, the contact lens which was removed from the eye is rubbed with a cleaning agent including a surface active agent, to thereby remove lipid stains deposited on the sufaces of the contact lens. If it is desired to remove protein stains, the contact lens is soaked in a cleaning agent including a proteolytic enzyme so as to remove the protein stains. After the contact lens is rinsed with a rinsing liquid, the contact lens is accommodated and stored in a container filled with a storing liquid. Since the microorganisms tend to adhere to and proliferate on the lens surfaces, especially where the contact lens is a water-containing or hydrogel lens, such water-containing or hydrogel contact lens needs to be disinfected by boiling. Namely, the hydrogel contact lens accommodated in a container requires a boiling procedure using a suitable boiling apparatus, in addition to the above-described procedure.
Thus, the procedure for treating the contact lenses is cumbersome, requiring several kinds of liquid agents such as a cleaning liquid and storing liquid, and a suitable apparatus for boiling the contact lenses. Accordingly, it is troublesome and costly for the contact lens users to treat the contact lenses.
For solving the above-described problem, there are proposed some methods for treating the contact lens in a simplified manner at a relatively low cost. These methods permit the contact lens to be treated by using a single liquid agent which is obtained by adding, to the storing liquid, a surface active agent, a protein removing agent, and a disinfectant. In these proposed methods, the contact lens is disinfected not by a thermal disinfecting method which requires the above-described boiling apparatus, but by a chemical disinfecting method using a disinfectant. Thus, the proposed methods eliminate the conventionally required boiling operation using the exclusive apparatus for boiling the contact lens, so as to facilitate the procedure for treating the contact lens.
The above-described contact lens liquid agent functions not only as a disinfectant which has a chemical disinfecting effect, but also as a storing liquid. Such a contact lens liquid agent is required to exhibit a high degree of sterilizing effect, and at the same time, a low degree of toxicity with respect to the eyes, since the contact lens is soaked in the liquid agent for a relatively long period of time.
As the disinfectant used in commercially available chemical disinfecting agents for the contact lens, thimerosal, chlorhexidine or quaternary ammonium salt (e.g., benzalkonium chloride) is used. In JP-A-52-109953, JP-A-62-153217 and JP-A-63-59960, there are proposed a disinfectant or liquid agent for contact lenses, which includes benzalkonium chloride in an amount of 0.001-0.2%, and a disinfectant for soft contact lenses, which includes chlorhexidine in an amount of 0.01-0.05%.
However, it is reported that such a disinfectant functions as an allergy intensifier and harms to the eyes of the user. Further, the disinfectant is adsorbed on or stored in the contact lens over a long period of use. For example, corneal troubles may be caused due to emission of the highly condensed disinfectant from the contact lens to the eye during wearing of the contact lens, or due to direct contact of the eye with the contact lens on which the disinfectant is adsorbed with high concentration ("Journal of Japan Contact Lens Society" 34:267-276, 277-282, 1992, 35:219-225, 1993, 36:57-61, 1994, 37:35-39, 154-157, 1995).
In an attempt to avoid such troubles, it may be considered to lower the concentration of the disinfectant to be used, for assuring a high degree of safety with respect to the eyes. In this case, however, the sterilizing action of the disinfectant is inevitably lowered, so that the contact lens may become contaminated with the microorganisms.